1. Field of the Invention
The present invention relates to a method of irradiating a running steel or other strip with energy beams. Energy-beam irradiation is performed by utilizing a plurality of individually located and oriented energy-beam irradiating devices and can be performed along the width of the strip even when an edge deviation or so-called "strip wind" occurs on the strip.
In accordance with the present invention, the strips used include not only metal strips such as cold-rolled steel sheet and aluminum sheet, but also various non-metal strips which are capable of running continuously along a production line.
The applied energy beam may include any irradiation beam emitted from plural energy sources using any of a variety of beam-like irradiations, such as electron beams, laser beams, plasma beams, or the like.
2. Description of the Related Art
Treatments for improving physical, chemical and surface characteristics of various strips or sheets are widely performed in various fields. For example, metallurgical, thermal and chemical treatments and the like are performed by irradiating strips or sheets with one or more of various energy beams.
In order to carry out these irradiations industrially, methods are available such as irradiating a running strip with a flat beam or a plurality of beams so as to cover the overall width of the strip, or the use of scanning beams arranged along the width of the strip.
The latter method is often used when the beam-generating device is expensive, when irradiation is performed with a view to improving the beam-focusing rate, or when the surface of the strip is intended to be irradiated with a plurality of different linear beams in order to finely divide the magnetic domain of a silicon steel sheet, for example, as disclosed in Japanese Patent Publication No. 2-40724, Japanese Patent Laid-Open No. 1-281708, or the like.
When energy-beam irradiation treatment of such a scanning type is applied to a wide strip running at a predetermined speed, such as a cold-rolling steel sheet, a plurality of individual energy-beam irradiating devices may be used according to the width of the strip.
Known energy-beam irradiation will now be described by way of an example using an electron-beam device as an energy-beam irradiating device.
FIGS. 1 and 2 of the drawings indicate a conventional method of uniformly scanning electron beams along the width of a strip by utilizing a plurality of electron-beam irradiating devices.
Although five electron-beam irradiating devices are shown as placed along the width of the strip in this example, two or more irradiating devices, or some other number, may be used.
FIGS. 1 and 2 indicate respectively electron-beam irradiating devices 1-5, an electron-beam controller 6 and a strip driving controller 7.
The strip irradiating beams are applied from the devices 1-5 in accordance with the width (W) obtained by taking the amount of linear deviation or strip winding into account, in addition to the width of the strip. According to a signal from the electron-beam controller 6, electron beams can be scanned along the width of the strip. The effective electron-beam irradiating device is selected with respect to the width W as follows (FIG. 1).
where W.ltoreq.W.sub.1 : Device 3 only PA1 where W.sub.1 .ltoreq.W.ltoreq.W.sub.2 : Devices 2-4 PA1 where W.sub.2 .ltoreq.W.ltoreq.W.sub.3 : Devices 1-5
where W.sub.1 shows the scannable width when only the electron-beam irradiating device 3 is desired to be used; W.sub.2 indicates the scannable width when the electron-beam irradiating devices 2-4 are desired to be used; and W.sub.3 represents the scannable width when all of the electron-beam irradiating devices 1-5 are desired to be used.
The irradiation con, and signal from controller 6 is controlled by the strip driving controller 7, taking the strip running speed into consideration. Further, the electron-beam irradiating regions are determined in real time, and the respective electron-beam scannings by the electron-beam irradiating devices 1-5 are constantly parallel to each other at a fixed pitch.
In the above conventional operation, since the actual amount of lateral deviation or winding of the strip is not taken into account, irradiation is performed within the regions of the scannable maximum values W.sub.1 -W.sub.3 of the selected electron-beam irradiating device.
These conventional methods of scanning electron beams by utilizing a plurality of electron-beam irradiating devices encounter important problems.
When a band-like strip is run continuously, it has been found that some amount of out-of-plane deformation of the sheet referred to as strip winding is caused by the conveying system, and cannot be avoided.
When the strip is run at a relatively low speed, the edge of the strip is clamped by a guide roller or the like, thereby inhibiting such strip winding. On the other hand, however, when the strip is run at a relatively high speed, considerable forces act upon the sheet, thus causing distortion or deformation. In such a case, the edge of the sheet simply cannot be clamped in place as a practical matter.
Instead, a so-called steering device has been tried to put a strip in the center of the line without touching the edge. However, even a high-cost and high-performance steering device cannot totally avoid sheet winding due to limited response and other causes. Further, when the strip itself possesses camber, the occurrence of strip winding is effectively unavoidable while continuously running.
In particular, when the electron-beam irradiating devices are longitudinally positioned in the machine direction to form steps, non-irradiated beam portions or overlapping-irradiated beam portions are produced in the vicinities of the borders between the neighboring irradiated regions on the strip, thus causing serious strip quality problems.
An electron-beam irradiating device requires very substantial peripheral space because of a vacuum system associated with it. Also, economical high-speed treatment of strip requires high energy density, and accordingly, the width scanned by one electron gun must be rather narrow.
Thus, electron-beam irradiating devices of the type described are normally longitudinally displaced along the machine direction to form steps in the high-speed treatment lines normally used.
As shown in FIG. 3, the electron-beam irradiating devices 1-5 are displaced to form steps along the strip running direction so that each irradiating device is displaced by the distance K. In this condition, when a strip wind shifts toward the "+" direction (toward the right in the drawing) such as to provide an amount of strip wind G within a distance M obtained by running the strip from the strip wind start point to the end point, non-scanned-omitted portions V.sub.1 -V.sub.4 are unavoidably produced due to the distance K, the displacement of the two neighboring irradiating devices.
In the stepped electron-beam irradiating devices of FIG. 3, when a strip wind shifts toward the "-" direction (toward the left in the drawing), the strip is scanned with overlapping.
A further problem occurs in irradiating edge regions. An electron-beam irradiating device is selected with the maximum width of a steel strip in mind, and irradiating as nearly as possible within the scannable maximum width. Hence, as shown in FIG. 2, the portions of the apparatus, for example, the strip support roll or the wall within the vacuum chamber, is repeatedly or continuously irradiated, seriously deteriorating these components and causing major problems of equipment maintenance.
In order to overcome the above problems, a beam-shielding cover is suggested, for example, in Japanese Patent Laid-Open No. 58-181820 However, such a shielding cover is not complete and the usage of high-energy beams requires a cooling unit, disadvantageously enlarging the device even more.
Further, when the amount of strip wind is unexpectedly increased, and consequently, the edge regions of the strip fall outside the scannable width of the pre-positioned electron-beam irradiating devices. The non-irradiated portions are produced at the edge of the strip, thus further causing serious problems in terms of the quality of the strip. The electron-beam devices cannot be modified easily.
Though irradiation has been described by using electron beams as energy beams, the application of laser beams or plasma beams also creates similar problems.